You can try and maybe nothing will happen but if it cracks you will have to dig it out.
Gap between tiles and wall.
This will give you say a perfect 3 8 caulk line with an irregular wall to counter gap.
Therefore the spacing is predetermined and usually averages 3 16 to 1 4 inch.
Your walls and floors are pretty stiff but there can be movement between the two that will crack the grout.
Your tile person will take the largest gap and run a tape line using that as the thickness or the caulk.
The tile council of north america recommends at least a quarter inch gap between the tile floor and the walls.
Fill gaps up to 1 4 inch in width with caulk.
When you install ceramic tile on the floor you must take care to create an expansion joint between the walls and the tiled floor.
The overall finish of your job really does depend on your own personal style.
Any gap should never be greater than 1 8 inch.
Instead fill it with an elastic material capable of sustaining the movement of the floor and the movement of the wall.
Two inch tiles are factory spaced and sheet mounted.
Tile stores generally sell caulks that match the grout.
If you have tile on the wall adjoining the tub select a caulk that matches the color of the grout.
For smaller tiles is advisable to use small spacers.
Four inch tiles called 4 and a quarter in the tile trade feature built in self fitting nubs that give the tiles spacing between 1 16 and 1 8 inch wide.
The large format 18 inch tiles should have inch space in between.
Caulking is the best choice for this application.
The line will continue maintaining caulk gap regardless of the gap of the wall to counter.
If your gap is smaller than 1 8 inch in width use.
Current trends are moving towards leaving much smaller grout lines between tiles.
Whenever tile has a right angle like that grout is prone to fail so caulk is used.
Ceramic tile wall gap back of tile should rest on finished wall.